New polyarylethersulfone circuit board substrates

ABSTRACT

Described herein are circuit board substrates prepared from certain poly(aryl ethers) based on 4,4&#39;-dichlorodiphenyl sulfone.

FIELD OF THE INVENTION

This invention relates to circuit boards prepared from certain poly(arylethers) based on 4,4'-dichlorodiphenyl sulfone.

BACKGROUND OF THE INVENTION

Circuit boards are widely used in the electrical industry for radio,television, computers, appliances, industrial and electronic equipment.Printed circuit boards have been traditionally manufactured from acopper clad epoxy-glass laminate. When starting with this material, theshape of the printed circuit board must first be routed out and theholes for mounting the components (e.g., transistors, resistors,integrated circuits, etc.) individually drilled. The board is thenmasked with photoresist, the circuitry imaged, and the copper etchedaway from areas where it is not wanted.

Another procedure for manufacturing printed circuit boards involvesinjection molding the circuit board substrate with the holes in place.The molded substrate is then put through several adhesion promotionsteps and plated with electroless copper according to standardtechnology, to produce the printed circuit board. In this injectionmolding procedure, the substrate material is limited to thermoplasticresins which resist blistering or distortion under the conditions neededfor soldering. In wave soldering, currently the dominant method, oneside of the plastic board briefly contacts an agitated pool of moltensolder, and heating of the board is localized. In the emerging surfacemount technologies, including vapor phase soldering (VPS), on the otherhand, the entire plastic board is exposed to temperatures of at least215° C. (419° F.). Obviously, savings result with these injection moldedcircuit board substrates due to the elimination of considerablemechanical processing such as routing and drilling.

The critical parameters of a printed circuit board, from a solderingstandpoint, are its glass transition temperature (Tg), environmentalstress crack resistance and thermal expansion coefficient. The higher asubstrate's glass transition temperature (Tg) and environmental stresscrack resistance to solder fluxes, the less likely it will blister ordelaminate during soldering.

Other parameters of a printed circuit board are its plateability andresistance to water absorption. Acceptable plateability requires goodadhesion of electrolessly plated copper to the circuit board substrate.Acceptable resistance to water absorption requires little or no waterassimilation into the circuit board substrate so as to provide goodelectrical properties.

Poly(aryl ether)s containing the following repeat units: ##STR1## arecommercially available thermoplastic polymers which have a wide varietyof end-use applications. These thermoplastic polymers are described in,for example, U. S. Pat. Nos. 4,175,175 (formula 1) and 4,008,203(formula 2). Such end-use applications include the use of thesethermoplastic polymers for injection molding into circuit boardsubstrates. However, a circuit board substrate molded from the poly(arylether) of formula (1) has a glass transition temperature (Tg) which isgenerally not as high as desired for soldering temperatures such asthose encountered in wave soldering. Circuit boards molded from thepoly(aryl ether) of formula (2) have an acceptable glass transitiontemperature (Tg) but do not have, in some instances, acceptableplateability and resistance to water absorption.

U.S. Pat. No. 4,520,067 describes a blend composition useful for makingcircuit board substrates and electrical connectors containing from 40 to90 weight percent of a poly(ether sulfone), i.e., such as that offormula (2) above, and from 10 to 60 weight percent of a polysulfone,i.e., such as that of formula (1) above. A circuit board substratemolded from the blend composition is stated to have improvedplateability.

U.S. patent application Ser. No. 448,376, filed Dec. 9, 1982, describesa blend composition useful for making circuit board substrates andelectrical connectors, containing a poly(aryl ether), i.e., such as thatof formulas (1) or (2) above, a poly(etherimide), fiber and a filler. Acircuit board substrate molded from the blended composition is stated tohave improved plateability.

U.S. patent application Ser. No. 011,898, filed Feb. 6, 1987, commonlyassigned, describes select poly(aryl ether sulfone) polymers useful formolding into a circuit board substrate. Incorporation of specifiedamounts of hydroquinone in the synthesis of a polymer such as that offormula (2) above, produces a poly(aryl ether sulfone) which is suitablefor being molded into circuit board substrates. When metal iselectroplated onto such circuit board substrates, it is stated thatthere is a high degree of adhesion of the metal to the circuit boardsubstrate.

U.S. Pat. No. 4,550,140 describes circuit board substrates prepared frompoly(aryl ethers) which contain repeating units derived frombis(3,5-dimethyl-4-hydroxyphenyl)sulfone. These substrates are claimedto exhibit adequate glass transition temperatures (Tg), acceptableplateability and acceptable resistance to water absorption.

DISCLOSURE OF THE INVENTION

It has been found as a result of this invention, that acceptable circuitboard substrates can be prepared from a composition comprising apoly(aryl ether) containing recurring units of the following formula:

    --O--E--O--E'--

wherein E' is the residiuum of 4,4'-dichlorodiphenyl sulfone, and E isselected from the roup of tetramethylbisphenol-A(TMBA), optionallyadmixed with up to 50 mole percent of a second diphenol, such as4,4'-biphenol or bisphenol-A; and from specified mixtures of

(a) 4,4'-dihydroxy diphenylsulfone(4,4,-bisphenol-S)/2,2-bis(4-hydroxyphenyl)propane (bisphenol-A);

(b) 4,4'-biphenol/bisphenol-A;

(c) 4,4'-biphenol/hydroquinone;

(d) 4,4'-biphenol/4,4'-bisphenol S; and

(e) hydroquinone/bisphenol-A.

The poly(aryl ethers) have a reduced viscosity of at least about 0.3dl/g as measured in N-methylpyrrolidone, at 25° C., at a concentrationof 1.0 g/100 ml. Circuit board substrates molded from these poly(arylethers) have desirable properties, including an adequate glasstransition temperature (Tg) and acceptable plateability and resistanceto water.

DETAILED DESCRIPTION OF THE INVENTION

The poly(aryl ether)s may be described as linear, thermoplasticpoly(aryl ether)s. They are generally prepared by reacting a dihydricphenol with an activated dihalo-substituted aromatic compound. Theessential feature of the poly(aryl ether) is the requirement that thepolymer chain contains repeating units derived from4,4'-dichlorodiphenyl sulfone (3). ##STR2## Specifically, the poly(arylether)s utilized in manufacturing the circuit board substrates of thisinvention contain recurring units of the following formula:

    --O--E--O--E'--

wherein E' is the residue of (3), e.g. (4) ##STR3## and E is the residueof a dihydric phenol. The dihydric phenol is selected from the groupconsisting of:

(a) tetramethylbisphenol-A, optionally containing up to 50 mole percentof 4,4'-biphenol and/or bisphenol-A; or

(b) mixtures of 4,4'-bisphenol-S and bisphenol-A containing from about60 to about 70 mole percent of bisphenol-A; or

(c) mixtures of 4,4'-biphenol and bisphenol-A containing from about 50to about 90 mole percent of 4,4'-biphenol; or

(d) mixtures of 4,4'-biphenol and hydroquinone containing from about 10to about 90 mole percent of 4,4'-biphenol; or

(e) mixtures of 4,4'-biphenol and 4,4'-bisphenol-S containing from about60 to about 90 mole percent of 4,4'-biphenol; or

(f) mixtures of hydroquinone and bisphenol-A containing from about 60 toabout 90 mole percent of hydroquinone.

It must be pointed out that the proportions of the diphenols given aboveare critical; small changes often lead to unsatisfactory results asillustrated in more detail below.

We note that the tetramethylbisphenol-A copolymers containingbisphenol-A and/or 4,4'-biphenol are new compositions of matter. Inaddition to being useful in circuit board applications, these poly(arylether)s display excellent mechanical properties and high glasstransition temperatures (>215° C.). In fact, as indicated by the data ofTable 6, these copolymers display better ductility and better toughnessthan the homopolyether from tetramethylbisphenol-A and4,4'-dichlorodiphenyl sulfone. These resins containing from about 5 to95, preferably from about 20 to about 80 mole percent of 4,4'-biphenoland/or bisphenol-A (based on total diphenols) are, therefore, usefulengineering thermoplastics in their own right.

The polymers of this invention may be prepared by either of two methods,i.e., the carbonate method or the alkali metal hydroxide method.

In the carbonate method, the polymers are prepared by contactingsubstantially equimolar amounts of the hydroxy-containing compounds anddihalodiarylsulfones, e.g., 4,4'-dichlorodiphenyl sulfone or4,4'-difluorodiphenyl sulfone, with from about 0.5 to about 1.0 mole ofan alkali metal carbonate per mole of hydroxyl group in a solventmixture comprising a solvent which forms an azeotrope with water inorder to maintain the reaction medium at substantially anhydrousconditions during the polymerization.

The temperature of the reaction mixture is kept at about 190° C. toabout 250° C., preferably from about 210° C. to about 240° C. for aboutone to 15 hours.

In a modification which is particularly suitable for making copolymersfrom bisphenol A and one or more additional dihydroxy compounds, thereactants other than said additional dihydroxy compounds are charged andheated at from about 120° C. to about 180° C. for about one to about 5hours, said additional dihydroxy compounds are added, the temperature israised and the mixture is heated at from about 200° C. to about 250° C.,preferably from about 210° C. to about 240° C., for about one to 10hours. This modification is further described in the copending U.S.patent application of Donald R. Kelsey, et al., Ser. No. 068,973, filedJuly 1, 1987, now U.S. Pat. No. 4,783,520, commonly assigned.

The reaction is carried out in an inert atmosphere, e.g., nitrogen, atatmospheric pressure, although higher or lower pressures may also beused.

The polyarylethersulfone is then recovered by conventional techniquessuch as coagulation, solvent evaporation, and the like.

The solvent mixture comprises a solvent which forms an azeotrope withwater and a polar aprotic solvent. The solvent which forms an azeotropewith water includes an aromatic hydrocarbon such as benzene, toluene,xylene, ethylbenzene, chlorobenzene, and the like.

The polar aprotic solvents employed in this invention are thosegenerally known in the art for the manufacture of polyarylether sulfonesand include sulfur containing solvents such as those of the formula:

    R.sub.1 --S(O).sub.b --R.sub.1

in which each R₁ represents a monovalent lower hydrocarbon group free ofaliphatic unsaturation, which preferably contains less than about 8carbon atoms or when connected together represents a divalent alkylenegroup with b being an integer from 1 to 2 inclusive. Thus, in all ofthese solvents, all oxygens and two carbon atoms are bonded to thesulfur atom. Contemplated for use in this invention are such solvents asthose having the formula: ##STR4## where the R₂ groups are independentlylower alkyl, such as methyl, ethyl, propyl, butyl, and like groups, andaryl groups such as phenyl and alkylphenyl groups such as the tolylgroup, as well as those where the R₂ groups are interconnected as in adivalent alkylene bridge such as: ##STR5## in tetrahydrothiophene oxidesand dioxides. Specifically, these solvents include dimethylsulfoxide,dimethylsulfone, diphenylsulfone, diethylsulfoxide, diethylsulfone,diisopropylsulfone, tetrahydrothiophene 1,1-dioxide (commonly calledtetramethylene sulfone or sulfolane) and tetrahydrothiophene-1 monoxide.

Additionally, nitrogen containing solvents may be used. These includedimethylacetamide, dimethylformamide and N-methylpyrrolidone.

The azeotrope forming solvent and polar aprotic solvent are used in aweight ratio of from about 1:10 to about 1:1, preferably from about 1:5to about 1:3.

In the reaction, the hydroxy containing compound is slowly converted, insitu, to the alkali salt thereof by reacting with the alkali metalcarbonate. The alkali metal carbonate is preferably potassium carbonate.Mixtures of carbonates such as potassium and sodium carbonate may alsobe used.

Water is continuously removed from the reaction mass as an azeotropewith the azeotrope forming solvent so that substantially anhydrousconditions are maintained during the polymerization.

It is essential that the reaction medium be maintained substantiallyanhydrous during the polycondensation. While amounts of water up toabout one percent can be tolerated, and are somewhat beneficial whenemployed with fluorinated dihalobenzenoid compounds, amounts of watersubstantially greater than this are desirably avoided as the reaction ofwater with the halo and/or nitro compound leads to formation of phenolicspecies and only low molecular weight products are secured.Consequently, in order to secure the high polymers, the system should besubstantially anhydrous, and preferably contain less that 0.5 percent byweight water during the reaction.

Preferably, after the desired molecular weight has been attained, thepolymer is treated with an activated aromatic halide or an aliphatichalide such as methyl chloride or benzyl chloride, and the like. Suchtreatment of the polymer converts the terminal hydroxyl groups intoether groups which stabilize the polymer. The polymer so treated hasgood melt and oxidative stability.

While the carbonate method for preparing the polymer of this inventionis simple and convenient, in some cases products of higher molecularweight can be made by the alkali metal hydroxide method. In the alkalimetal hydroxide method, described by Johnson et al., U.S. Pat. Nos.4,108,837 and 4,175,175, a double alkali metal salt of a dihydric phenolis contacted with a dihalobenzenoid compound in the presence of a sulfurcontaining solvent as herein above defined under substantially anhydrousconditions.

Additionally, the polymers of this invention may be prepared by othermethods known in the prior art, in which at least one dihydric phenoland at least one dihalobenzenoid compound are heated, for example, witha mixture of sodium carbonate or bicarbonate and a second alkali metalcarbonate or bicarbonate having a higher atomic number than that ofsodium, as described in U.S. Pat. No. 4,176,222.

The molecular weight of the poly(aryl ether)s utilized in manufacturingthe circuit board substrates of this invention is indicated by reducedviscosity data in N-methylpyrrolidone. As well understood in the art,the viscosity of a resin solution bears a direct relationship to theweight average molecular size of the polymer chains, and is typicallythe most important single property that can be used to characterize thedegree of polymerization. The reduced viscosity assigned to thepoly(aryl ether)s is therefore to be understood as significant inreflecting molecular weight rather than a consideration concerning theviscosity per se. Most of these poly(aryl ether) polymers are readilysoluble in N-methylpyrrolidone, chloroform, or tetrachloroethane orother similar solvents.

Reduced viscosity (R.V.) as used in the examples herein was determinedby dissolving a 1.0 gram sample of the poly(aryl ether) polymer inN-methylpyrrolidone contained in a 100 milliliter volumetric flask sothat the resultant solution measured exactly 100 milliliters at 25° C.in a constant temperature bath. The viscosity of 3 milliliters of thesolution which had been filtered through a sintered glass funnel wasdetermined in an Ostwald or similar type viscometer at 25° C. Reducedviscosity values were obtained from the equation: ##EQU1## wherein:t_(o) is the efflux time of the pure solvent;

t_(s) is the efflux time of the polymer solution; and

C is the concentration of the polymer solution expressed in terms ofgrams of polymer per 100 milliliters of solution.

The poly(aryl ether)s utilized in manufacturing the circuit boardsubstrates of this invention are characterized as linear thermoplasticstructures which have a relatively high molecular weight, that is, areduced viscosity determined at a concentration of 1.0 g/100 ml inN-methylpyrrolidone at 25° C. of at least 0.3 dl/g, preferably at least0.5 dl/g and, typically, not exceeding about 1.5 dl/g. These polymersprovide highly desirable properties to circuit boards preparedtherefrom. Circuit board substrates molded from these poly(aryl ether)shave an adequate glass transition temperature (Tg), acceptableplateability and acceptable resistance to water absorption.

In order to determine the usefulness of the polymers for circuit boardapplications the polymers were tested by simulated vapor phase soldering(VPS) of samples which had been saturated with water. Molded specimenswere immersed in water under ambient temperature and were weighedperiodically until they appeared to have absorbed an equilibrium amountof water. The wet samples were then immersed in a fluorocarbon vapor at215° C. for a predetermined length of time, removed, and examined. Thesamples were divided into three classes:

Class 1: little or no deformation;

Class 2: minor surface deformation, may have fine interior bubbles;

Class 3: severe deformation, often including large bubbles.

Experience has shown that polymers of Class 1 and Class 2, but not Class3, can be formulated to give molded circuit boards which can be solderedwithout preliminary drying.

The results of the VPS test cannot be predicted from the structure andother properties of the polymers. The glass transition temperature ofthe polymer, the amount of water absorbed, the mechanism and rate ofwater evolution, the extent to which the glass transition temperature isaltered by the presence of water, and probably other unknown factors,all influence the behavior of the circuit board substrate under VPSconditions. The test itself is an excellent simulation of actualprocessing conditions and shows that VPS behavior may be affected inunpredictable ways by relatively small changes in composition. Thus, asshown in Example 1 and Comparative Examples A and B, a copolymer madefrom 65 mole percent bisphenol S and 35 mole percent bisphenol A gaveClass 2 performance, whereas the analogous copolymers containing 85 or50 mole percent bisphenol S were rated Class 3.

The poly(aryl ether)s utilized in manufacturing the circuit boardsubstrates of this invention may be optionally used with otheringredients such as stabilizers, i.e., metal oxides such as zinc oxide,antioxidants, flame retardants, pigments, and the like. The poly(arylether)s may be optionally used with reinforcing fibers and/or inorganicfillers. The reinforcing fiber includes fiberglass, carbon fibers, andthe like, and mixtures thereof. The carbon fibers include those having ahigh Young's modulus of elasticity and high tensile strength. Thesecarbon fibers may be produced from pitch, as described in U.S. Pat. Nos.3,976,729; 4,005,183 and 4,026,788, for example. The particulateinorganic fillers which may be used include wollastonite, calciumcarbonate, glass beads, talc, mica, clay, quartz and the like, ormixtures thereof.

The fiber reinforcement, filler or combinations thereof, can be utilizedin amounts of from 0 to about 50 weight percent, preferably from about10 to about 35 weight percent, of the total weight of the circuit boardsubstrate.

The poly(aryl ether)s in combination with other ingredients can beprepared by any conventional mixing methods. For example, the poly(arylether)s and other optional ingredients in powder or granular form can beblended in an extruder and the mixture can be extruded into strands andthe strands can be chopped into pellets. The pellets can then be moldedinto the desired circuit board substrate by conventional techniques.

The poly(aryl ether)s can be molded into circuit board substrates usingconventional techniques such as injection molding or via extrusion ofsheets.

Specifically, the composition can be processed into circuit boardsubstrates using conventional molding equipment or die punching of theextruded sheets. The molded boards may then be swelled and etched topromote the adhesion of copper by both roughening the surface andintroducing chemical moieties through oxidation if electrolessdeposition is to be utilized. The circuitry is then applied to the boardvia either conventional electroless deposition, vacuum deposition,sputtering, or via the use of polymer thick film materials orcombinations thereof.

As used in this invention, the glass transition temperature (Tg) of thepolymers herein has a direct correlation with the heat distortiontemperature of the polymers. In general, the heat distortion temperatureof the polymers is typically 10° C. to 20° C. below the glass transitiontemperature (Tg) of the amorphous polymers.

Although the invention has been described with respect to a number ofdetails, it is not intended that this invention should be limitedthereby. The examples which follow are intended solely to illustrate theembodiments of this invention which to date have been determined and arenot intended in any way to limit the scope and intent of this invention.

The glass transition temperature (Tg) of the polymers prepared in theexamples was measured by the resilience minimum technique usingmodulus-temperature data and resilience-temperature data as described inO. Olabisi et al., "Polymer-Polymer Miscibility", Academic Press, NewYork, 1979, pages 122-126.

EXAMPLES

The following examples serve to give specific illustrations of thepractice of this invention but they are not intended in any way to limitthe scope of this invention.

EXAMPLE 1 65/35 Molar 4,4'-Dihydroxydiphenyl Sulfone/(4,4'-Bisphenol A)Dichlorodiphenylsulfone Copolymer

In a 500 ml, four-necked flask equipped with a stainless steelmechanical stirrer, a thermocouple, an addition funnel, and a Claisenarm fitted with a nitrogen inlet tube, a distillation trap, a condenserand an exit gas bubbler, were placed the following materials:

13.53 g (59.3 mmole) bisphenol A,

48.82 g (170.0 mmole) 4,4'-dichlorodiphenylsulfone,

24.91 g (180.2 mmole) anhydrous potassium carbonate,

181. g sulfolane, and

75. g toluene.

The mixture was heated under a nitrogen atmosphere; distillation oftoluene and water began at 130° C. When the temperature reached 160° C.,dropwise addition of toluene was started, and the temperature wasmaintained at 160°-163° C. for two hours. Toluene addition was stopped,the heating source was removed, and 4,4'-bisphenol S (27.55 g, 110.1mmole) was added and rinsed in with about 10 ml of toluene. Heating wasresumed, and toluene addition was restarted at 220° C. The mixture wasmaintained at 227°-233° C. for 4.5 hours and then allowed to cool toroom temperature overnight. On the following day, the mixture wasreheated to 200° C., addition of a mixture of sulfolane (30 g) andchlorobenzene (110 g) was started, and methyl chloride was sparged intothe solution to endcap the polymer. The solution was further dilutedwith chlorobenzene (100 g) and then filtered hot through a bed of filteraid on a medium porosity fritted-glass funnel. The polymer was recoveredby coagulation in a Waring blender, washed thoroughly with water andmethanol, and dried in a vacuum oven at about 150° C. Yield 55.4 g(71.4%), reduced viscosity (measured in N-methylpyrrolidone, 1 g/dl, at25° C.) 0.70 dl/g. The composition of the diphenol mixture used to makethis copolymer was 65 mole percent 4,4'-bisphenol S/35 mole percentbisphenol A. The results of water absorption/vapor phase soldering testson 4,4'-bisphenol S/bisphenol A-dichlorodiphenylsulfone copolymers aregiven in Table 1. The polymer of Example 1 gave satisfactory performancein the vapor phase soldering test and was rated Class 2.

Comparative Example A

An 85/15 molar 4,4'-bisphenol S/bisphenol A-dichlorodiphenylsulfonecopolymer was prepared by essentially the same method as that ofExample 1. The reduced viscosity, measured in N-methylpyrrolidone (0.2g/dl at 25° C.), was 0.54 dl/g. As shown in Table 1, this polymer gaveunsatisfactory performance in the vapor phase soldering test and wasrated as Class 3.

Comparative Example B

A 50/50 molar 4,4'-bisphenol S/bisphenol A-dichlorodiphenyl sulfonecopolymer was made by a process similar to that of Example 1 except thatall of the reactants were charged to the reactor at the beginning of therun. Its reduced viscosity (0.2 g/dl in N-methylpyrrolidone at 25° C.)was 0.52 dl/g. As shown in Table 1, this polymer gave unsatisfactoryperformance in the vapor phase soldering test and was rated as Class 3.

EXAMPLE 2 60/40 Molar 4,4'-Biphenol/Bisphenol A-DichlorodiphenylsulfoneCopolymer

In an apparatus similar to that used in Example 1, were charged:

16.44 g (72.0 mmole) 4,4'-bisphenol A,

51.92 g (180.8 mmole) 4,4'-dichlorodiphenylsulfone,

29.98 g (216.9 mmole) anhydrous potassium carbonate,

160. g sulfolane, and

160. g chlorobenzene

This mixture was stirred and heated under a nitrogen atmosphere.Distillation of water and chlorobenzene began when the temperaturereached 149° C. When the temperature reached 170° C., dropwise additionof chlorobenzene was begun, and the temperature was maintained at170°-172° C. for one hour. The heating source was removed andchlorobenzene addition stopped. 4,4'-Biphenol (20.12 g, 108.1 mmole) wasadded and rinsed in with chlorobenzene (about 10 ml), and thetemperature was raised to 220° C. Chlorobenzene addition was resumed,and the temperature was maintained at 218°-220° C. for five hours. Thepolymer was endcapped and recovered essentially as in Example 1. Yield50.6 g (67.2%), reduced viscosity (1 g/dl in N-methylpyrrolidone at 25°C.) 0.61 dl/g. The composition of the diphenol mixture used to make thiscopolymer was 60 mole percent 4,4'-biphenol/40 mole percent bisphenol A.Test results on the 4,4'-biphenol/bisphenol A-dichlorodiphenylsulfonecopolymers are given in Table 2.

EXAMPLE 3 75/25 Molar 4,4'-Biphenol/Hydroquinone-DichlorodiphenylsulfoneCopolymer

In an apparatus similar to that used for Example 1, were placed thefollowing materials:

27.82 g (149.4 mmole) 4,4'-biphenol,

5.48 g (49.8 mmole) hydroquinone,

57.43 g (200.0 mmole) 4,4'-dichlorodiphenylsulfone,

29.30 g (212.0 mmole) anhydrous potassium carbonate,

178. g sulfolane, and

76. g chlorobenzene.

The mixture was heated under nitrogen, a mixture of water andchlorobenzene starting to distill off at 160° C. The reaction mixturewas stirred at 219°-221° C. with dropwise chlorobenzene addition for 3hours. The polymer was endcapped and recovered essentially as inExample 1. Yield 43.6 g (57.3%), reduced viscosity (1 g/dl inN-methylpyrrolidone at 25° C.) 0.54 dl/g. The composition of thediphenol mixture used to make this copolymer was 75 mole percent4,4'-biphenol/25 mole percent hydroquinone. The test results on the4,4'-biphenol/hydroquinone dichlorodiphenylsulfone copolymers are givenin Table 3.

EXAMPLE 4 75/25 Molar 4,4'-Biphenol/4,4'-BisphenolS-Dichlorodiphenylsulfone Copolymer

In an apparatus similar to that used in Example 1 were placed:

22.83 g (122.6 mmole) biphenol,

10.23 g (40.9 mmole) 4,4'-bisphenol S,

46.94 g (163.5 mmole) 4,4'-dichlorodiphenylsulfone,

27.14 g (196.4 mmole) anhydrous potassium carbonate,

145. g sulfolane, and

145. g chlorobenzene.

The mixture was stirred and heated under a nitrogen atmosphere; waterand chlorobenzene began to distil off at 148° C. At 213° C. addition ofchlorobenzene was begun. The mixture was maintained for 1.5 hours at212°-214° C. with chlorobenzene addition and then for an additional 4hours at 214° C. without it. The polymer was endcapped and recoveredessentially as in Example 1. Yield 43.6 g (64.0%), reduced viscosity (1g/dl in N-methylpyrrolidone at 25° C.) 0.67 dl/g. The composition of thediphenol mixture used to make the copolymer was 75 mole percent4,4'-biphenol/25 mole percent 4,4'-bisphenol S. The results on the4,4'-biphenol/4,4'bisphenol S-dichlorodiphenylsulfone copolymers aregiven in Table 4.

EXAMPLE 5 80/20 Molar Hydroquinone/Bisphenol A-DichlorodiphenylsulfoneCopolymer

In an apparatus similar to that used in Example 1 were placed thefollowing materials:

19.30 g (175.3 mmole) hydroquinone,

10.01 g (43.8 mmole) bisphenol A,

63.18 g (220.0 mmole) 4,4'-dichlorodiphenylsulfone,

33.45 g (242.0 mmole) anhydrous potassium carbonate,

179. g sulfolane, and

77. g chlorobenzene.

The mixture was heated under a nitrogen atmosphere; distillation ofchlorobenzene and water began at 160° C. At 220° C. dropwise addition ofchlorobenzene was begun, and the temperature was held at 220° C. for 4.5hours. The polymer was endcapped and recovered essentially as inExample 1. Yield 47.85 g (62.5%), reduced viscosity (1 g/dl inN-methylpyrrolidone at 25° C.) 0.52 dl/g. The composition of thediphenol mixture used to make this copolymer was 80 mole percenthydroquinone/20 mole percent bisphenol A. The results on thehydroquinone/bisphenol A-dichlorodiphenylsulfone copolymers are given inTable 5.

EXAMPLE 6 70/30 Molar TetramethylbisphenolA/Biphenol-Dichlorodiphenylsulfone Copolymer

The apparatus for this procedure consisted of a 500 ml, four-neckedglass flask equipped with a stainless steel mechanical stirrer, athermocouple probe, addition funnels of various sizes, an inlet tube forsparging gas below the liquid surface, and a Dean-Stark trap surmountedby a reflux condenser vented through a gas bubbler; heating wasaccomplished by an oil bath. In the flask were placed:

44.80 g (157.5 mmole) 4,4'-isopropylidenebis-(2,6-dimethylphenol)(tetramethylbisphenol A),

140. g toluene,

124. g dimethylsulfoxide, and

12.57 g (67.5 mmole) 4,4'-biphenol.

This mixture was stirred and heated under a nitrogen atmosphere. To itwas added over 8 minutes at 40°-49° C. aqueous sodium hydroxide (49.47%,36.31 g, 447.8 mmole); the contents of the addition funnel were rinsedin with a total of about 6 ml of hot deionized water. Temperature wasraised over 29 minutes to 109° C. and then over 1.5 hours to 122° C.while water was periodically drained from the Dean-Stark trap. Toluenewas then removed over 27 minutes, the temperature rising to 160° C. Ahot solution of 4,4'-dichlorodiphenylsulfone (64.62 g, 225.0 mmole) intoluene (75 ml) was then added over 25 minutes at a reactor temperatureof 160° C., and the addition funnel was rinsed with about 10 ml of hottoluene. The mixture was stirred for 4 hours at 160°-162° C., becomingvery viscous. To it were added in quick succession aqueous sodiumhydroxide (49.47%, 0.19 g, 2.3 mmole), hot deionized water (about 1 ml),and toluene (5 ml). The added water was readily removed by distillation.The mixture was stirred about one hour longer at 160° C., then allowedto cool overnight. On the second day, chlorobenzene (195 g) was added,and the temperature was raised to 130° C. to effect complete solution.Methyl chloride was sparged in for one hour at 111°-114° C. to endcapthe polymer; then oxalic acid 1.0 g (11 mmole) was added, and themixture was stirred for 30 minutes at 109°-111° C. The solution wasfiltered through a layer of filter aid on a coarse porosityfritted-glass funnel. The polymer was recovered by coagulation in aWaring blender, washed thoroughly with water and methanol, and dried ina vacuum oven at about 150° C. Yield 66.98 g (63.4%), reduced viscosity(1 g/dl in N-methylpyrrolidone at 25° C.) 0.53 dl/g. The composition ofthe diphenol mixture used to make this copolymer was 70 mole percenttetramethylbisphenol A/30 mole percent bisphenol. Test results on thepolymer containing tetramethylbisphenol A are given in Table 6.

EXAMPLE 7 60/40 Molar Tetramethylbisphenol A/BisphenolA-Dichlorodiphenylsulfone Copolymer

The procedure of Example 6 was followed with a diphenol mixtureconsisting of

38.39 g (135 mmole) tetramethylbisphenol A, and

20.55 g (90 mmole) bisphenol A.

Yield 67.66 g (63.1%), reduced viscosity (1 g/dl in N-methylpyrrolidoneat 25° C.) 0.72 dl/g. The composition of the diphenol mixture used tomake this copolymer was 60 mole percent tetramethylbisphenol A/40 molepercent bisphenol A. Test results are given in Table 6.

EXAMPLE 8 Tetramethylbisphenol A-Dichlorodiphenylsulfone Polymer

The procedure of Example 6 was followed with the diphenol consistingsolely of tetramethylbisphenol A (63.99 g, 225.0 mmole). Yield 67.1 g(59.8%), reduced viscosity (1 g/dl in N-methylpyrrolidone at 25° C.)0.71 dl/g. Physical properties of the tetramethylbisphenol A polymersand results of the water absorption/vapor phase soldering tests aregiven in Table 6. The data indicate that the copolymers have a yieldpoint and therefore undergo ductile failure, whereas thetetramethylbisphenol A homopolymer exhibits brittle failure. The impactstrengths of the copolymers are also much higher than that of thehomopolymer.

                  TABLE 1                                                         ______________________________________                                        Mole %                 Equilib. Water                                         Bisphenol S                                                                           Bisphenol A                                                                              Tg, °C.                                                                        Absorption, %                                                                           VPS Class                                ______________________________________                                        100      0         220     2.31      3                                        85      15         220     1.92      3                                        70      30         215     1.68      2                                        65      35         215     1.56      2                                        57      43         205     1.44      2 (quite                                                                      good)                                    50      50         205     1.19      3                                         0      100        190     0.76      3                                        ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Mole %                 Equilib. Water                                         Biphenol                                                                             Bisphenol A                                                                              Tg, °C.                                                                         Absorption, %                                                                           VPS Class                                ______________________________________                                        100     0         220      1.23      3                                        75     25         205      1.05      2                                        60     40         205      1.02      2                                        50     50         200      0.98      2                                         0     100        190      0.76      3                                        ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Mole %                 Equilib. Water                                         Biphenol                                                                             Hydroquinone                                                                              Tg, °C.                                                                        Absorption, %                                                                           VPS Class                                ______________________________________                                        100     0          220     1.23      3                                        75     25          212     1.21      2                                        50     50          205     1.22      2                                        20     80          210     1.32      2                                        ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Mole %                Equilib. Water                                          Biphenol                                                                             Bisphenol S                                                                              Tg, °C.                                                                        Absorption, %                                                                            VPS Class                                ______________________________________                                        100     0         220     1.23       3                                        75     25         220     1.52       2                                         0     100        220     2.31       3                                        ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        mole %                    Equilib. Water                                                                            VPS                                     Hydroquinone                                                                            Bisphenol A                                                                              Tg, °C.                                                                         Absorption, %                                                                           Class                                 ______________________________________                                        90        10         195      1.23      2                                     80        20         195      1.12      2                                     70        30         195      1.14      2                                     60        40         195      1.06      2                                      0        100        190      0.76      3                                     ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Example:       6        7           8                                         ______________________________________                                        Comonomer:     Biphenol Bisphenol A None                                      Mole %         30       40          --                                        Tg, °C. 230      220         235                                       Yield Strength, psi                                                                          11,700   11,200      --                                        Tensile Strength, psi                                                                        11,700   11,200      11,100                                    Yield Elongation, %                                                                          7.3      7.4         --                                        Elongation at Break, %                                                                       9.2      11.0        6.3                                       Pendulum Impact,                                                                             61       39          7                                         ft-lb/in.sup.3                                                                Water absorption, %                                                                          0.97     0.90        0.91                                      VPS Class      1        1*          1                                         ______________________________________                                         *No distortion, but a few bubbles.                                       

What is claimed is:
 1. A circuit board substrate molded from acomposition comprising a poly(aryl ether) containing recurring units ofthe formula

    --O--E--O--E'--

wherein E is the residuum of ##STR6## a mixture of dihydric phenolsselected from the group consisting of tetramethylbisphenol-A and up to50 mole percent of 4,4'-biphenol, tetramethylbisphenol-A and up to 50mole percent of bisphenol-A, and tetramethylbisphenol-A and up to atotal of 50 mole percent of 4,4'-biphenol and bisphenol-A; and whereinE' is the residuum of 4,4'-dichlorodiphenyl sulfone; and wherein thepoly(aryl ether) has a reduced viscosity of at least 0.3 dl/g, asmeasured in N-methylpyrrolidone at a concentration of 1.0 g/100 ml at25° C.
 2. A circuit board substrate molded from a composition comprisinga poly(aryl ether) containing recurring units of the formula

    --O--E--O--E'--

wherein E is the residuum of mixtures of 4,4'-dihydroxydiphenyl sulfoneand bisphenol-A containing from about 60 to about 70 mole percent ofbisphenol-A; and wherein E, is the residuum of 4,4'-dichlorodiphenylsulfone; and wherein the poly(aryl ether) has a reduced viscosity of atleast 0.3 dl/g, as measured in N-methylpyrrolidone, at a concentrationof 1.0 g/100 ml. at 25° C.
 3. A circuit board substrate molded from acomposition comprising a poly(aryl ether) containing recurring units ofthe formula

    --O--E--O--E'--

wherein E is the residuum of mixtures of 4,4'-biphenol and bisphenol-Acontaining from about 50 to about 90 mole percent of 4,4'-biphenol; andwherein E' is the residuum of 4,4'-dichlorodiphenyl sulfone; and whereinthe poly(aryl ether) has a reduced viscosity of at least 0.3 dl/g, asmeasured in N-methylpyrrolidone, at a concentration of 1.0 g/100 ml. at25° C.
 4. A circuit board substrate molded from a composition comprisinga poly(aryl ether) containing recurring units of the formula

    --O--E--O--E'--

wherein E is the residuum of mixtures of 4,4'-biphenol and hydroquinonecontaining from about 10 to about 90 mole percent of 4,4'-biphenol; andwherein E' is the residuum of 4,4'-dichlorodiphenyl sulfone; and whereinthe poly(aryl ether) has a reduced viscosity of at least 0.3 dl/g, asmeasured in N-methylpyrrolidone, at a concentration of 1.0 g/100 ml. at25° C.
 5. A circuit board substrate molded from a composition comprisinga poly(aryl ether) containing recurring units of the formula

    --O--E--O--E'--

wherein E is the residuum of mixtures of 4,4'-biphenol and4,4'-dihydroxydiphenyl sulfone containing from about 60 to about 90 molepercent of 4,4'-biphenol; and wherein E' is the residuum of4,4'-dichlorodiphenyl sulfone; and wherein the poly(aryl ether) has areduced viscosity of at least 0.3 dl/g, as measured inN-methylpyrrolidone, at a concentration of 1.0 g/100 ml. at 25° C.
 6. Acircuit board substrate molded from a composition comprising a poly(arylether) containing recurring units of the formula

    --O--E--O--E'--

wherein E is the residuum of mixtures of hydroquinone and bisphenol-Acontaining from about 60 to about 90 mole percent of hydroquinone; andwherein E' is the residuum of 4,4'-dichlorodiphenyl sulfone; and whereinthe poly(aryl ether) has a reduced viscosity of at least 0.3 dl/g, asmeasured in N-methylpyrrolidone, at a concentration of 1.0 g/100 ml at25° C.
 7. A circuit board substrate as defined in claims 1 or 2 or 3 or4 or 5 or 6 wherein the composition contains up to about 50 weightpercent of a mineral filler.
 8. A circuit board substrate as defined inclaim 7 wherein the mineral filler is selected from wollastonite,calcium carbonate, glass beads, talc, mica, clay and quartz.
 9. Acircuit board substrate as defined in claims 1 or 2 or 3 or 4 or 5 or 6wherein the composition contains up to about 50 weight percent of areinforcing fiber.
 10. A circuit board substrate as defined in claim 9wherein the reinforcing fiber is selected from fiberglass and carbonfibers.
 11. A circuit board substrate molded from a compositioncomprising a poly(aryl ether) containing recurring units of the formula

    --O--E--O--E'--

wherein E is the residuum of a mixture of dihydric alcohols selectedfrom the group consisting of tetramethylbisphenol-A and up to 50 molepercent of 4,4'-biphenol, tetramethylbisphenol-A and up to 50 molepercent of bisphenol-A, tetramethylbisphenol-A and up to a total of 50mole percent of 4,4'-biphenol and bisphenol-A, 4,4'-bisphenol-S andbisphenol-A containing from about 60 to about 70 mole percent ofbisphenol-A, 4,4'-biphenol and bisphenol-A containing from about 50 toabout 90 mole percent of 4,4'-biphenol, 4,4'-biphenol and hydroquinonecontaining from about 10 to about 90 mole percent of hydroquinone,4,4'-biphenol and 4,4'-bisphenol-S containing from about 60 to about 90mole percent of 4,4'-biphenol, and, hydroquinone and bisphenol-Acontaining from about 60 to about 90 mole percent of hydroquinone; andwherein E' is the residuum of 4,4'-dichlorodiphenyl sulfone; and whereinthe poly(aryl ether) has a reduced viscosity of at least 0.3 dl/g, asmeasured in N-methylpyrrolidone at a concentration of 1.0 g/100 ml at25° C.